Aerosol composition for forming a hydrated membrane, and applications thereof

ABSTRACT

The present invention relates to an aerosol composition for forming a preferably hydrated membrane which after vaporizing comprises as least one hydrophobic phase containing at least one film-forming polymer at least partly solubilized in an organic solvent system. The polymer is selected from hydrophobic polyaminoacids, preferably from the polyaminoacids obtained from at least one of the amino acids alanine, valine, leucine, isoleucine, proline, methionine, phenylalanine, tryptophan, aspartic and glutamic acid esters, or the derivatives thereof. The compositions also comprises as least one hydrophilic phase, and at least one propellant. The preferably hydrated membrane formed by vaporizing this composition, the application of the composition and of the preferably hydrated membrane as a dressing, are also disclosed.

This application is a 371 of PCT/FR94/01123 filed Sep. 27, 1994.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the present invention is that of aerosol compositions andmore particularly those consisting of propelled film-forming substanceswhich are useful especially, but not exclusively, for the application ofa curative protective film to lesions, for example skin lesions.

More precisely, the present invention relates to an aerosol compositionfor forming a preferably hydrated membrane.

The invention further relates to the preferably hydrated membraneobtained from the abovementioned aerosol composition.

Without implying a limitation, the invention relates more specificallyto the application of this aerosol composition and this preferablyhydrated membrane for the dressing of wounds, burns or the like.

2. Description of the Prior Art

The purpose of dressing these local traumatisms, often on the skin, isto protect them from the external environment so as to avoid bacterialcontamination and allow rapid healing of high quality. To this end, thedressing should obviously be biocompatible so as to be perfectlytolerated, and should preferably be transparent so that the conditionand progress of the traumatism can be checked easily.

It is also advantageous for the dressing to possess a degree ofmechanical strength, to be permeable to water vapor and also to be easyand painless to apply and remove.

The most traditional dressing is the one consisting of gauze (optionallymounted on adhesive plastic tape). The major disadvantage of this typeof dressing is that it adheres too strongly to the wound, whereby thechanges of dressing, which are of necessity relatively frequent, aredelicate and painful operations. Moreover, the dressed lesions are inmost cases suppurant, causing obstruction of the gauze or similardressing. The dressing consequently becomes impermeable, therebydetracting from the healing and curing of the lesion.

Propelled film-forming substances for dressings are also known whichconsist of aerosol compositions comprising an active polymer as thefilm-forming substance, said polymer being capable of forming, aftervaporization, a biocompatible film which adheres conveniently to theskin and is transparent and elastic, to name only some of theabovementioned properties expected for application as a dressing.

A wide variety of aerosol compositions containing a film-forming polymerhave already been proposed. The following examples may be mentioned:

a composition containing polyvinyl acetate, polyvinylpyrrolidone andacetic acid (cf. FR-A-1 589 917),

a composition based on curable polysiloxane, of the two-component type,associated with a propellant gas (cf. FR-A-2 589 737),

a composition consisting of polyacrylates or methacrylates, ethylcellulose, polyvinylbutyral, an ethylene oxide copolymer or apolyisobutylene in solution in solvent such as butanol (cf. FR-A-2 219793 and FR-A-2 212 134),

or else a composition containing an ammonium salt of organosiliconcompounds bonded to organic polymers such as polyvinylpyrrolidone orcellulose acrylate or methacrylate, associated with a solvent propellant(cf. U.S. Pat. No. 4,921,691).

The constituent polymers of these known aerosol compositions have thedisadvantage of producing non-hydrated films which are not entirelysatisfactory in terms of healing. Moreover, it is clear that, in allprobability, these polymers comprise unnatural residual monomers whichare capable of generating inflammatory reactions on account of theirtoxicity towards a living medium (e.g. acrylic derivatives andsiloxanes).

In an attempt to improve these vaporizable aerosol compositions fordressings, EP-A-0 521 455 has proposed replacing the known, imperfectfilm-forming polymers with a biodegradable hydroxycarboxylic acidpolymer. The polymer in question can be a polylactic and/or polyglycolicpolymer dissolved in a propellant solvent such as dimethyl ether, afreon, a gaseous alkane (e.g. liquefied propane) or an analog of saidsolvents. This aerosol composition also comprises water and an alcoholsuch as ethanol, which is useful as a solvent for various therapeuticactive principles which may be present.

Despite the advantages of their biocompatibility and biodegradability,these hydroxycarboxylic acid polymers suffer from a serious shortcomingassociated with the quality of the film they can produce aftervaporization. In fact, it is found that the aerosol compositions basedon these hydroxycarboxylic acid polymers are the center of a macroscopicphase separation during vaporization, the consequence of which is toeliminate the water to give a dry film. Such a product seems to berather unsuitable for the dressing of wounds, burns or the like becauseits excessively anhydrous nature means that it either has difficultyadhering to the wound or adheres to it too strongly, which causesdifficulties and pain when the film is detached.

There is therefore an obvious need for an aerosol composition based on abiocompatible, biodegradable and non-toxic polymer and pharmaceuticallyacceptable excipients which, on vaporization, can produce inter aliadressings in the form of films, the latter meeting specificationsappropriate to this application:

cohesion,

permeability to water vapor and oxygen,

impermeability to bacteria,

biocompatibility, tolerance and non-toxicity,

healing promoter,

analgesic,

convenient adhesion to the damaged area, while remaining detachable withease and without pain, and

preferably a hydrated state which provides a degree of flexibility and adegree of elasticity and which accelerates the curing process (M. F.JONKMAN in "High Performance Biomaterials", Ed. M. Szycher, Technomic(1991)).

A solid form of dressing or temporary skin substitute is known which hasall these properties; it is in the form of a flexible, translucent,colorless membrane marketed under the name INERPAN®. This skinsubstitute consists of a leucine/methyl glutamate copolymer impregnatedwith a liquid based on polyethylene glycol, sodium chloride and purifiedwater.

Although INERPAN® has demonstrated perfectly its efficacy for thedressing of burns and bedsores in particular, it only exists in the formof thick membranes of predetermined dimensions. Moreover, theapplication of this dressing requires cautious manipulation and use,limiting its use in today's hospital environment.

It follows from the above that the development of a polymer formulationbased on amino acids which formed a film on vaporization would be atotally desirable and valuable technical development, particularly inthe field of human health and especially with a view to application as adressing.

The spray form of a biocompatible, preferably hydrated membrane wouldrepresent a novel product, both in design and in realization, and wouldhave the following advantages over the presently known, conventional,non-vaporizable dressings based on hydrogel membranes:

a low unit treatment cost because-of the small amount of productrequired per dressing, and substantial ease of use, which would make theproduct suitable for use by the general public, and

variety and flexibility as regards the size of the dressings (surfacearea and thickness).

Consequently, one of the essential objectives of the invention is toprovide a pharmaceutically acceptable aerosol composition for forming ahydrated membrane after vaporization, said membrane being usableespecially as a dressing and possessing the properties referred toabove, particularly those of a cohesive, preferably hydrated,biocompatible and therapeutically effective film. To achieve this andother objectives, the Applicant succeeded, after numerous experimentsand studies, in solving the problem of which some of the aspects are asfollows:

to render compatible a mixture of a hydrophobic phase containing afilm-forming polymer, and a hydrophilic phase, so as to preventprecipitation of the polymer and allow simultaneous vaporization ofthese two phases to give a membrane,

to give this membrane good cohesion, and

preferably, to ensure that this membrane is suitably hydrated.

SUMMARY OF THE INVENTION

The solution to this problem consists particularly in producing themixture of a hydrophobic phase containing the film-forming polymer, anda hydrophilic phase, and in selecting the film-forming polymer frompolyamino acids.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention thus relates to an aerosol composition for forminga preferably hydrated membrane after vaporization, characterized in thatit comprises:

at least one hydrophobic phase containing a hydrophobic polyamino acidwhich is at least partially solubilized in an organic solvent system andis preferably selected from polyamino acids obtained from at least oneof the following hydrophobic amino acids or derivatives: alanine,valine, leucine, isoleucine, proline, methionine, phenylalanine,tryptophan and aspartic and glutamic acid esters,

at least one, preferably aqueous, hydrophilic phase, and

at least one propellant.

Such an aerosol composition is particularly advantageous as a dressingsince, on the one hand, it is easy and painless to apply to the lesionand, on the other hand, the film obtained after spraying contains atleast one hydrophilic product and/or at least one liquid and/or retainsthe water initially present, at least for a few minutes, so that apreferably hydrated membrane forms.

This preferably hydrated polymer film is non-toxic and non-irritant andmay be transparent. It favors healing and is easy and painless to detachfrom the lesion.

These results are particularly surprising and unexpected insofar as thestructural polyamino acid(s) contained in the hydrophobic phase is (are)incompatible with the aqueous phase or with other components of thecomposition, such as the propellant. It was therefore difficult toimagine a priori:

1--how to vaporize both the hydrophobic and hydrophilic phasessimultaneously,

2--how to obtain a cohesive film rather than a mass of individualparticles, and

3--how the polymer could trap the water after vaporization andevaporation of the solvent.

Yet it is found that simple shaking of the polyphase mixture accordingto the invention gives an emulsion which, after vaporization, produces amoist, cohesive and homogeneous film. Contrary to all expectations, thisemulsion does not require the incorporation of surfactants; furthermore,no precipitation of the polymer is observed. It is self-evident that theinvention is not thereby limited to compositions without surfactants. Itis indeed possible for the latter to be adjuvants in said compositions.

The polyamino acid selected according to the invention can be ahomopolymer or a copolymer of hydrophobic amino acids preferablyselected from those mentioned above. In the present disclosure, thesehomopolymers and copolymers will be referred to indiscriminately by theterm polymer.

In one advantageous modality of the invention, the content ofhydrophobic amino acids in the polyamino acid is greater than or equalto 5% by number and preferably greater than or equal to 15% by number.

These polymers have a sufficient molecular weight to give the body andtexture of a membrane to the materials obtained by vaporization of theaerosol composition of the invention. As a general indication, thismolecular weight can vary approximately from 10³ to 15×10⁵ andpreferably from 4×10⁴ to 3×10⁵ D.

Polymers of leucine and/or glutamic acid alkyl esters (preferablymethyl, ethyl or benzyl esters) are preferentially chosen as thepolyamino acid. In the case of a copolymer, for example Leu/Glu(OMe),the respective relative proportions, expressed in mol, are between 99/1and 1/99, preferably between 30/70 and 70/30 and particularly preferablybetween 45/55 and 55/45.

According to the invention, the aerosol composition can comprise asingle polymer or a mixture of polymers.

As far as the synthesis of these polymers is concerned, it should bestated that it is perfectly known per se. Thus, for example, thepolymers used in the composition of the invention can be those describedin the following patent applications: GB 996 760 and FR 1 603 159.

The polymer or polymers are present in the aerosol composition in anamount of 0.05 to 30% by weight/weight, based on the total amount ofaerosol.

Expressed differently, the concentration of the polymer in thehydrophobic organic phase is between 0.1 and 40, preferably between 0.5and 10 and particularly preferably between 0.5 and 4% by weight/volume,based on the solvent system.

In one advantageous modality of the invention, the organic solventsystem of the hydrophobic phase consists of at least one ether, onehalogenoalkane, one halogenoalkene or one halogenoaromatic compound, orelse a mixture thereof.

In practice, the solvent system is preferably chosen from the followingcompounds:

chlorofluorocarbons and analogs,

hydrogenofluorocarbons and analogs,

chlorocarbons and analogs,

acetals,

ethers,

esters,

ketones,

alcohols, and

mixtures thereof,

trichlorofluoromethane, dichlorodifluoromethane,1-chloro-1-difluoroethane, methyl formate, methylal and dimethyl etherbeing particularly preferred.

In another advantageous modality of the invention, the mass ratio of thehydrophobic organic phase to that of the hydrophilic phase, expressed inpart by weight, is set between 100/1 and 1/1, preferably between 50/1and 1/1 and particularly preferably between 20/1 and 2/1.

The propellant used to ensure vaporization of the composition preferablyconsists of at least one liquefied or non-liquefied, pressurized gaspreferably selected from the following list of products: propane,butane, isobutane, nitrogen, CO₂, dimethyl ether, halogenoalkanes (e.g.chlorofluorocarbons or analogs) and mixtures thereof.

To simplify the composition, it is advantageous if at least part of thesolvent system acts as both solvent and propellant simultaneously.

In practice, and out of concern for the environment, it is possible touse gases and/or solvents which are not aggressive towards the ozonelayer.

The amount of propellant is not an essential datum of the composition ofthe invention but, as an illustrative indication, it is generallybetween 1 and 99% by weight/weight, preferably between 40 and 90% byweight/weight, based on the total amount of aerosol.

The hydrophilic phase of the composition is preferably aqueous. In thecontext of optimization of the aerosol composition of the invention, ithas been shown to be of particular value, in certain cases, toincorporate adjuvants into the aqueous phase.

In particular, the presence of C₁ to C₁₀ lower alcohols, such as ethanolor propanol, is sometimes desirable for improving the solubilization ofsome of the constituents of the aerosol composition.

Ethanol is preferably selected from among the abovementioned loweralcohols which can be incorporated into the composition.

Certain adjuvants can be useful for increasing the water retentioncapacity of the preferably hydrated membrane obtained after vaporizationof the aerosol composition of the invention. Such functional adjuvantscan be chosen from among the known products. According to the invention,it is more preferable to select polyols such as glycerol, glycols, or"polymeric" alcohols such as polyglycols like polyethylene glycol orpolypropylene glycol, of variable molecular weights.

The concentrations of these adjuvants in the composition areadvantageously

from 0.1 to 10%, preferably from 0.5 to 5%, in the case of loweralcohols, and

from 0 to 50%, preferably 5 to 10%, in the case of polymeric alcohols.

To perfect the therapeutic efficacy of the aerosol composition of theinvention in its application as a dressing, one or more activeprinciples of a pharmaceutical or cosmetic nature, for example, can beadded thereto.

This active ingredient can be e.g. a disinfectant for external use ofthe known and/or marketed type, a bactericide, fungicide or virucide, ananalgesic, an antiinflammatory, a hemostat or any other compound whichis useful for preparing drugs for external use.

The active principles can also be of a cosmetic nature, such as sunprotection products or even insect repellents.

It should be noted that the abovementioned functional adjuvants canserve to solubilize some of the abovementioned active principles.

In a preferred mode of carrying out the invention:

the hydrophobic organic phase of the composition comprises

a polymer of leucine and/or of a glutamic acid alkyl ester, and

a solvent consisting of a pressurized mixture of dimethyl ether andmethylal, which also acts as propellant,

while its hydrophilic phase contains water, and

a polyol, preferably a polyethylene glycol,

said composition optionally containing one or more of the activeprinciples referred to above.

It is self-evident that various other products or excipientstraditionally employed in aerosol compositions can be added to thiscomposition.

This aerosol composition is prepared in conventional manner by bringingtogether the polymer and the solvent and then incorporating the aqueousphase and the propellant gas under pressure. The container used is aconventional aerosol can crimped just before injection of the liquidpropellant gas under pressure.

The vaporization of this composition, which is preferably emulsifiedbeforehand by shaking, takes place in conventional manner by theformation of a mist of microdroplets of variable size. In one variant,and by extrapolation, the vaporization can be compared to a shot ofliquid.

According to another of its aspects, the invention relates to thepreferably hydrated membrane obtained by vaporization of the aerosolcomposition described above. It is clear that the aerosol composition isperfectly suitable and appropriate for the formation of a hydrated film,but it is perfectly possible to envisage producing this film from a foamor a cream.

The film obtained by vaporization is advantageously flexible and moist.This moisture is preferably obtained at least partly by hydration. Thehydration time depends on the one hand on the water evaporation rate, anunavoidable phenomenon at room temperature, and on the other hand on thewater retention capacity of the membrane, which, as has been seen, canbe adjusted with the aid of functional adjuvants like polyethyleneglycol.

Industrial Application

Apart from application as a dressing (wounds, burns, dermatology,treatment of sunstroke, etc.), the composition according to theinvention can find valuable outlets particularly in the fields of thecontrolled release of active principles (transdermal systems) and thesurface treatment of biomaterials (to render them biocompitible).

The present invention will be understood more clearly and its advantagesand practical variants will become apparent from the following Examplesdescribing the preparation of aerosol compositions and the production ofpreferably hydrated dressings by vaporization.

EXAMPLES General Considerations

In the Examples which follow, the aerosol composition according to theinvention is prepared by bringing the polymer Leu/Glu(OMe) into contactwith a liquefied gas under pressure. The addition of polyethylene glycol(PEG) and water (or only one of the two) leads to the formation of afluid emulsion which can readily be vaporized. This emulsion separatesin a few hours but a homogeneous mixture is restored by shaking the can.It is not necessary to add surfactants in order to obtain this effect.During vaporization, part of the solvent system evaporates and thetreated surface is covered with a continuous, thin film (about 30 μm),which is of variable moisture content and transparency depending on theexact composition of the formulation. After about 60 seconds, the filmis sufficiently solid to be lifted and repositioned. When used as adressing, this film adheres sufficiently well to the skin and is removedeasily, and also painlessly, under a stream of water.

Example 1

1. 0.35 g of copolymer Leu/Glu(OMe) of molar composition 49/51 and ofreduced viscosity 0.8 dl/g is weighed out.

2. 27 ml of freon 11 and 1.3 ml of ethanol are added and the mixture isshaken until all the polymer has dissolved. This gives a viscous andslightly opaque solution.

3. The solution is diluted by the addition of 18 ml of freon 11.

4. 4.6 g of water and 7.6 g of PEG 600 are added to the polymer solutionand the aerosol can is crimped and shaken to form the emulsion.

5. 42 g of freon 22 are injected under pressure and the can is shaken.

A hydrated, flexible and transparent film is obtained after spraying.

Example 2

Procedure according to Example 1, the copolymer being a copolymerLeu/Glu(OMe) 47/53 of reduced viscosity 1.9 dl/g. A hydrated, flexibleand transparent film is obtained.

Example 3

Procedure according to Example 1 but without the addition of water. Aflexible and transparent membrane is obtained.

Example 4

1.01 g of polymer Leu/Glu(OMe) of molar composition 47/53 and of reducedviscosity 2.0 dl/g are weighed out. 20.26 g of methyl formate and 0.7 gof PEG 600 are added. The aerosol valve is crimped on and the can isshaken until dissolution is complete. 13.76 g of standardbutane/isobutane/propane mixture are then injected (2.5 bar). Acontinuous, flexible and strong film is obtained after spraying onto theskin.

Example 5

0.81 g of polymer Leu/Glu(OMe) of molar composition 47/53 and of reducedviscosity 2.0 dl/g is weighed out. 14.94 g of methylal(dimethoxymethane) are added and the aerosol valve is crimped on. Aftershaking until dissolution is complete, 30 g of dimethyl ether areinjected, followed by 4.20 g of a PEG 600/water mixture of composition63/37% w/w. A continuous, flexible and hydrated film is obtained afterspraying onto the skin.

Example 6

1.01 g of polymer Leu/Glu(OMe) of molar composition 47/53 and of reducedviscosity 2.0 dl/g are weighed out. 20.26 g of methyl formate and 0.70 gof PEG 600 are added. The aerosol valve is crimped on. After shakinguntil dissolution is complete, 13.76 g of a butane/isobutane/propanemixture are injected under pressure (2.5 bar). A continuous and flexiblefilm is obtained after spraying onto the skin.

What is claimed is:
 1. An aerosol composition for forming a membraneafter vaporization, comprisingat least one hydrophobic phase containingat least one hydrophobic polyamino acid which is at least partiallysolubilized in an organic solvent system, at least one hydrophilicphase, and at least one propellant wherein:(i) the hydrophobic aminoacid in the polyamino acid is present in at least 5% by number; (ii) thepolyaminoacids have a molecular weight of 10³ to 15×10⁵ D; (iii) thepolyaminoacids are present in an amount of 0.05-30% (w/w), based on thetotal amount of the aerosol; (iv) the polyaminoacids are present in thehydrophobic phase in an amount of 0.1-40% (w/v), based on the solventsystem; (v) the hydrophobic organic phase and the hydrophilic phase havea mass ratio of 100:1 to 1:1; (vi) the propellant comprises at least oneliquefied or non-liquefied, pressurized gas; and (vii) the propellant ispresent in an amount of 1-99% (w/w) based on the total amount ofaerosol.
 2. A composition according to claim 1 devoid of water andcomprising:in its hydrophobic organic phase:a polymer of leucine and/orof a glutamic acid alkyl ester, and a solvent selected from the groupconsisting of dimethyl ether, methylol, methyl formate and mixturesthereof, in its hydrophilic phase:polyethylenglycol, polypropyleneglycolor a mixture thereof; a propellant; and optionally one or more activeprinciples.
 3. A composition according to claim 1 wherein the solventsystem comprisesat least one compound selected from the class of ethersand/or halogenoalkanes and/or halogenoalkenes and/or halogenoaromaticcompounds.
 4. A composition according to claim 1 wherein the propellantis a pressurized gas.
 5. A composition according to claim 1 wherein theaqueous phase contains aduvants.
 6. A composition according to claim 1wherein at least one, active principle is added thereto.
 7. Acomposition according to claim 1 whereinits hydrophobic organic phasecomprisesa polymer of leucine and/or of a glutamic acid alkyl ester, anda solvent consisting of a pressurized mixture of dimethyl ether andmethylal, which also acts as propellant, its hydrophilic phasecontainswater, and a polyol, and it optionally contains one or moreactive principles.
 8. A membrane which it is obtained by vaporization ofthe aerosol composition according to claim
 1. 9. Application of thecomposition according to claim 1, as a dressing, as a transdermal systemfor the controlled release of active principles or in the surfacetreatment of biomaterials.
 10. Application of the membrane according toclaim 8 as a dressing, as a transdermal system for the controlledrelease of active principles, or in the surface treatment ofbiomaterials.
 11. A composition according to claim 1 wherein themembrane is hydrated.
 12. A composition according to claim 1 wherein thepolyamino acid is composed of amino acid selected from the groupconsisting of alanine, valine, leucine, isoleucine, proline, methionine,phenylalanine, tryptophan, aspartic acid esters, glutamic acid esters,and mixtures thereof.
 13. A composition according to claim 1 wherein thehydrophilic phase is aqueous.
 14. A composition according to claim 1wherein the content of hydrophobic amino acids in the polyamino acid isgreater than or equal to 15% by number.
 15. A composition according toclaim 1 wherein the concentration of the polymer in the hydrophobicorganic phase is between 0.5 and 10% by weight/volume.
 16. A compositionaccording to claim 1 wherein the concentration of the polymer in thehydrophobic organic phase is between 0.5 and 4% by weight/volume.
 17. Acomposition according to claim 1 wherein the solvent system comprisesatleast one compound selected from the class of ethers and/orhalogenoalkanes and/or halogenoalkenes and/or halogenoaromaticcompounds, and at least one chlorofluorocarbon or analog, onehydrogenofluorocarbon or analog, one chlorocarbon or analog, one acetal,one ether, one ester, one ketone, one alcohol or a mixture thereof. 18.A composition according to claim 1 wherein the solvent system comprisestrichlorofluoromethane, dichlorofluoromethane,1-chloro-1-difluoroethane, methylformate, methylal, dimethyl ether or amixture thereof.
 19. A composition according to claim 5, wherein thepressurized gas is selected from the group consisting of propane,butane, isobutane, nitrogen, CO₂, dimethyl ether, halogenoalkanes andmixtures thereof.
 20. A composition according to claim 5 wherein theadjuvants are alcohols.
 21. A composition according to claim 5 whereinthe adjuvants are selected from the group consisting of ethanol,propanol, glycols, polyglycols, polyols and mixtures thereof.
 22. Acomposition according to claim 1 wherein the mass ratio of hydrophobicorganic phase to hydrophilic phase, expressed in parts by weight, isbetween 50/1 and 1/1.
 23. A composition according to claim 1 wherein themass ratio of hydrophobic organic phase to hydrophilic phase, expressedin parts by weight, is between 20/1 and 2/1.
 24. A composition accordingto claim 6 wherein the active principle is a pharmaceutical or cosmeticingredient.
 25. A composition according to claim 7 wherein the polyol isa polyethylene glycol.
 26. A composition according to claim 1 whereinthe propellant is selected from the group consisting of propane, butane,isobutane, nitrogen, CO₂, dimethyl ether, halogenoalkanes and mixturesthereof.
 27. A composition according to claim 24, wherein the activeprinciple is selected from the group consisting of disinfectants,bactericides, fungicides, virucides, analgesics, anti-inflammatories,hemostats, sun protection products, insect repellents, and mixturesthereof.
 28. A membrane according to claim 8 which is hydrated.
 29. Anapplication as claimed in claim 10 wherein the membrane is hydrated. 30.An aerosol composition for forming a membrane after vaporizationcomprising:at lease one hydrophobic phase containing at least onehydrophobic polyamino acid which is at least partially solubilized in anorganic solvent system, at least one hydrophilic phase, wherein(I) thehydrophobic amino acid in the polyamino acid is present in at least 5%by number; (ii) the polyaminoacids have a molecular weight of 10³ to15×10⁵ D; (iii) the polyaminoacids are present in an amount of 0.05-30%(w/w), based on the total amount of the aerosol; (iv) the polyaminoacidsare present in the hydrophobic phase in an amount of 0.1-40% (w/v),based on the solvent system; (v) the hydrophobic organic phase and thehydrophilic phase have a mass ratio of 100:1 to 1:1.
 31. A compositionaccording to claim 30 comprising water.
 32. A composition according toclaim 30 wherein the hydrophilic phase contains water.
 33. A compositionaccording to claim 30 which does not comprise water.
 34. A compositionaccording to claim 30 wherein at least part of the solvent system actsas both solvent and propellant simultaneously.
 35. A compositionaccording to claim 30 wherein the solvent system at least one compoundselected from the group consisting of ethers, halogenoalkanes,halogenoalkenes, halogenoaromatic compounds and mixtures thereof.
 36. Acomposition according to claim 30 wherein at least part of the solventsystem acts as both solvent and propellant simultaneously.
 37. Acomposition according to claim 30 wherein the aqueous phase containsadjuvants.
 38. A composition according to claim 30 wherein at least oneactive principle is added thereto.
 39. A composition according to claim30 wherein:its hydrophobic organic phase comprisesa polymer of leucineand/or of a glutamic acid alkyl ester, and a solvent consisting of apressurized mixture of dimethyl ether and methylal, which also acts aspropellant, its hydrophilic phase containswater, and a polyol, and itoptionally contains one or more active principles.
 40. A membrane thatit is obtained by vaporization of the aerosol composition according toclaim
 30. 41. A method for the surface treatment of biomaterials whichcomprises applying the composition according to claim 30 as atransdermal system for the controlled release of active principles forthe surface treatment of biomaterials.
 42. A method of dressing byapplying the membrane according to claim 40 as a dressing, as atransdermal system for the controlled release of active principles, orin the surface treatment of biomaterials.
 43. A composition according toclaim 30 wherein the membrane is hydrated.
 44. A composition accordingto claim 30 wherein the polyamino acid is obtained from alanine, valine,leucine, isoleucine, proline, methionine, phenylalanine, tryptophan,aspartic acid esters, glutamic acid esters, or mixtures thereof.
 45. Acomposition according to claim 30 wherein the content of hydrophobicamino acids in the polyamino acid is greater than or equal to 15% bynumber.
 46. A composition according to claim 30 wherein theconcentration of the polymer in the hydrophobic organic phase is between0.5 and 10% by weight/volume.
 47. A composition according to claim 30wherein the concentration of the polymer in the hydrophobic organicphase is between 0.5 and 4% by weight/volume.
 48. A compositionaccording to claim 30 wherein the solvent system comprises:at least onecompound selected from the group consisting of ethers, halogenoalkanese,halogenoalkenes, halogenoaromatic compounds and mixtures thereof, and atleast one chlorofluorocarbon or analog, one hydrogenofluorocarbon oranalog, one chlorocarbon or analog, one acetal, one ether, one ester,one ketone, one alcohol or a mixture thereof.
 49. A compositionaccording to claim 30 wherein the solvent system comprisestrichlorofluoromethane, dichlorofluoromethane,1-chloro-1-difluoroethane, methylformate, methylal, dimethyl ether or amixture thereof.
 50. A composition according to claim 37 wherein theadjuvants are alcohols.
 51. A composition according to claim 37 whereinthe adjuvants are selected from the group consisting of ethanol,propanol, glycols, polyglycols, polyols and mixtures thereof.
 52. Acomposition according to claim 30 wherein the mass ratio of hydrophobicorganic phase to hydrophilic phase, expressed in parts by weight, isbetween 50/1 and 1/1.
 53. A composition according to claim 30 whereinthe mass ratio of hydrophobic organic phase to hydrophilic phase,expressed in parts by weight, is between 20/1 and 2/1.
 54. A compositionaccording to claim 38 wherein the active principle is a pharmaceuticalor cosmetic ingredient.
 55. A composition according to claim 39 whereinthe polyol is a polyethylene glycol.
 56. A composition according toclaim 30 wherein the propellant is selected from the group consisting ofpropane, butane, isobutane, nitrogen, CO₂, dimethyl ether,halogenoalkanes and mixtures thereof.
 57. A composition according toclaim 54, wherein the active principle is selected from the groupconsisting of disinfectants, bactericides, fungicides, virucides,analgesics, anti-inflammatories, hemostats, sun protection products,insect repellents, and mixtures thereof.